The present invention relates to an anti-counterfeiting multiple-image display body for ID cards, passports, and banknotes.
It is desirable that counterfeiting be difficult for items including negotiable instruments such as coupons and checks; cards such as credit cards, cash cards, and ID cards; certificates such as driver's licenses and passports; brand name products; electronic gadgets; and personal authentication media. Such items may thus use display bodies that have superior anti-counterfeiting effects.
Such display bodies often include fine structures (i.e., optical elements) such as diffraction gratings, holograms, and lens arrays. The optical elements, for example, cause dynamic pattern changes when the observation angle changes. This hinders analysis and counterfeiting. Accordingly, such optical elements have a relatively high anti-counterfeiting effect.
In the prior art, there are image display bodies that use optical elements such as those described above. For example, Japanese National Phase Laid-Open Patent Publication No. 2009-543138 describes an image display body that stacks lens array layer and an icon layer to produce continuous movement and create a sense of depth. Such an image display body has been put to practical use due to its high anti-counterfeiting effect.
The image display body of Japanese National Phase Laid-Open Patent Publication No. 2009-543138 is an extremely thin film of 50 μm or less to allow for applications that watermark paper used for currency. This requires extremely high precision for the focal distance of lenses, the size of the lens array, and the icon size so that a high anti-counterfeiting effect can be obtained.
However, with a multiple-image display body including a lens array in a surface layer, contamination of the lens layer in the outermost surface layer by a liquid such as oil or a chemical would result in defects such as loss of the lens effect (condensing effect, magnifying effect) and loss of the desired continuous movement and depth in a display. Such a defect may lead to an authentication failure during actual use of ID cards, passports, and banknotes.
To resolve this defect, WO2011/007343A1 proposes a stacked display body that does not use lenses. The display body of WO2011/007343A1 is a stacked display body that includes a transmittive “line tone barrier layer,” a “spacer layer,” and a “multiple-image formation layer.” The multiple-image formation layer is divided into multiple images at a line tone pitch. Further, the display body is a multiple-image display body of a parallax barrier type that allows for the appearance of multiple images recorded on the “multiple-image formation layer” when viewed over the “line tone barrier layer” in accordance with the observed angle.
The structure of WO2011/007343A1 does not cause a loss in the desired continuous movement and depth of a display even when the uppermost layer is contaminated by a liquid such as oil or a chemical. This is sufficient for actual use in ID cards, passports, or banknotes.
However, the outermost “line tone barrier layer” decreases the light intensity. Thus, it is difficult for the multiple-image display body to show the “multiple images” of a lower layer with sufficient contrast.
Further, authentication that uses transmission light (for example, authentication using watermark) obtains satisfactory contrast. This allows the multiple-image display body to obtain a display effect that produces continuous movement and depth. However, in authentication that uses reflection light, insufficient light intensity lowers the contrast of the lower layer images. This causes difficulties in authentication.